He's (at least) implicitly saying that KhanAcademy sucks. I didn't really read it too too carefully, but that's the sense I get from it. He seems to be pissed about an error that Sal made, and is jumping to conclusions saying that KhanAcademy sucks. To make that claim, you'd have say what it means to suck, and why KhanAcademy does so (DH6).